1. Field of the Invention
The present invention relates to a display substrate, a display panel including the display substrate, and a method of testing a display substrate. More particularly, the present invention relates to a display substrate having a substantially enhanced reliability, a display panel including the display substrate, and a method of testing a display substrate.
2. Description of the Related Art
Display devices such as monitors and television sets, for example, have an ongoing need for continually-improved characteristics such as having increasingly small sizes and light weights. As a result, cathode ray tube (“CRT”) devices are being increasingly replaced with alternative display devices, such as liquid crystal display (“LCD”) devices. However, an LCD device requires an additional light source, since a display panel of the LCD device is not self-emissive. Further, the LCD device has a relatively low response speed and a relatively narrow viewing angle, for example, in comparison with some other types of display devices.
An organic light-emitting diode (“OLED”) display device has been identified as another relatively small and lightweight alternative to CRT devices. The OLED display device emits light by itself, e.g., is self-emitting, and the OLED display device also has a relatively wide viewing angle and a relatively high contrast ratio, for example, in comparison with an LCD device. Furthermore, since the OLED display device does not require an additional light source such as backlight assembly, the OLED display device is also relatively lightweight and consumes relatively low power in comparison with the LCD device. Additionally, the OLED display device has a relatively high response speed, a relatively wide operating temperature range and a relatively low manufacturing cost, for example, in comparison with the LCD device.
The OLED display device typically includes two electrodes and a light-emitting layer disposed therebetween. When an electron, injected from a first electrode, is coupled in a light-emitting layer with an imaginary particle (called an electron hole) injected from a second electrode, an exciton is formed. The exciton then releases energy to emit light and display an image.
The OLED display device is classified as either an active matrix type OLED display device or a passive matrix type OLED display device, based on a configuration of switching devices in the respective display device. Specifically, the active matrix type OLED display device includes a switching thin-film transistor (“TFT”) and a driving TFT for each light-emitting element. In the active matrix type OLED, the switching TFT is electrically connected to a signal wire which supplies a data voltage. The driving TFT applies the data voltage to a control electrode to cause a current to flow in a given light-emitting element.
Operational characteristics of the OLED display device are determined by driving characteristics of the switching TFT, the driving TFT and the light-emitting element. As a result, operational reliability of the OLED display device is determined by the driving characteristics of the switching TFT, the driving TFT and the light-emitting element. However, it is difficult to determine the driving characteristics of the switching TFT, the driving TFT and the light-emitting element of a given OLED device during a manufacturing process of the given OLED display device.